One of the most persistent issues in psychiatric epidemiology centers on social class: Are rates of some types of psychiatric disorder higher in lower social classes because of greater social stress; or are rates higher because genetically predisposed persons are selected into or fail to rise out of lower class environments? The proposed five year study would use a quasi-experimental strategy to test these contrasting social stress-social selection explanations. The strategy involves comparisons of advantaged and disadvantaged ethnic groups with social class controlled, and tests of related predictions concerning group differences in the types and magnitudes of stressful life events experienced. Israel would be the research setting. There are two main reasons for this choice: First, the quasi-experimental strategy requires an open society in which ethnic assimilation is taking place. Second, study of the processes involved and their consequences can best be accomplished when a well kept Population Register and Psychiatric Register are available. Israel, probably uniquely, meets both sets of requirements. In Israel, relatively disadvantaged African and Asian Jews would be compared with relatively advantaged Jews of European origin in investigations of interrelated samples of adult subjects ranging in size from a few hundred to about 7500. Main focus would be on a carefully stratified probability sample of 2200 subjects drawn from the Population Register; these subjects would be studied prospectively by psychiatrists and clinical psychologists over the period of a year. Comparisons would be made of true (untreated as well as treated) rates of clinically diagnosed schizophrenia, affective psychosis, antisocial personality, alcoholism or drug addiction, and neurosis, as well as for certain types of empirically derived symptom clusters. The main measuring instrument would consist of the Psychiatric Epidemiology Research Interview (PERI) that is based on our methodological research over the past 10 years together with Wing's PSE or Spitzer et al.'s SADS.